1. Field of the Invention
The present invention relates in general to the field of information handling system displays and, more particularly, to a system and method for improving the display of motion video on an LCD panel.
2. Description of the Related Art
As the value and use of information continues to increase, individuals and businesses seek additional ways to process and store information. One option available to users is information handling systems. An information handling system generally processes, compiles, stores, and/or communicates information or data for business, personal, or other purposes thereby allowing users to take advantage of the value of the information. Because technology and information handling needs and requirements vary between different users or applications, information handling systems may also vary regarding what information is handled, how the information is handled, how much information is processed, stored, or communicated, and how quickly and efficiently the information may be processed, stored, or communicated. The variations in information handling systems allow for information handling systems to be general or configured for a specific user or specific use such as financial transaction processing, airline reservations, enterprise data storage, or global communications. In addition, information handling systems may include a variety of hardware and software components that may be configured to process, store, and communicate information and may include one or more computer systems, data storage systems, and networking systems.
Information handling systems configured as portable units have grown in popularity among users over the past several years. Portable information handling systems generally integrate in a single housing a display, internal power source and processing components, such as the CPU and hard disk drive, so that a user can carry the portable system from place to place while the system is operating. As processing components have decreased in size and increased in performance, portable information handling systems are often able to pack processing capabilities into a relatively small housing that are comparable to the capabilities available from desktop systems. Generally, the most practical display solution for portable systems both in terms of size and power consumption are liquid crystal display (LCD) panels.
These LCD panels are progressively scanned, meaning that at any given time instant, partial frames of both the previous and current frame are visible on the screen along with a progressively moving tear boundary. This scan and hold characteristic is well suited for the display of static image content, such as spreadsheets and word processing documents, since screen flicker is minimal compared to cathode ray tube (CRT) displays. In the past, video content viewed on LCD panels was generally of low quality and/or resolution, and typically limited to game graphics, Internet video streams, and file-based video clips. Today it is becoming common to use LCD panels for delivery of high quality video content. However, the same characteristics that are well suited for display of static content are undesirable for display of video that contains motion. In general, this is due to the inadequate pixel response times of liquid crystal display (LCD) panels.
Each pixel in an LCD consists of a column of liquid crystal molecules suspended between two transparent electrodes that are in turn sandwiched between two polarizing filters whose axes of polarity are perpendicular to each other. By applying voltage to the transparent electrodes over each pixel, the corresponding liquid crystal molecules are “twisted” by electrostatic forces, allowing varying degrees of light to pass through the polarizing filters. Due to their electro-optical nature, the liquid crystal materials used in LCD panels have inertia and cannot be switched instantaneously. This results in transition response times that are generally not fast enough for high quality video applications. This slow response time, or latency, can result in video motion artifacts that cause quickly moving objects to appear visually blurred, an effect known as “ghosting” or “smearing.”
LCD response times continue to improve, but vendor specifications are generally limited to “off-to-on,” “rise and fall,” or “black-to-white” response time, which is the time it takes a pixel to change from black to white (rise) and then back to black (fall). The voltage required to change an LCD pixel from black to white, or white to black is greater than the voltage to change a pixel from one shade of grey to another. This disparity in voltage differential is the reason “black-to-white” response time is much faster than “grey-to-grey” response time, which is defined as the time it takes a pixel to change from one shade of grey to another. Grey-to-grey response times for LCD panels typically used in portable information handling systems can be many times longer (e.g., 30 to 50 msec.) than corresponding “black-to-white” response times.
Video frame rates are typically on the order of 17 msec at 60 Hz, which can be shorter than liquid crystal “grey-to-grey” response time. These frame rates, when combined with motion within the video frame, can result in video artifacts that cause smearing and low video quality. This problem extends to all LCD displays, but it is more of an issue for LCD panels used in portable information processing systems due to their typically lower power consumption and correspondingly slow response times. In addition, due to limited battery life, power adapter capacity, cooling limitations, fan noise and other operational and design constraints known to those of skill in the art, portable systems are generally designed to efficiently use computation cycles and minimize the associated overhead required to display an image.
Current approaches to pixel response time issues include LCD Response Time Compensation (LRTC), an approach for mitigating video artifacts that can contribute to smearing when motion video is displayed on an LCD screen. LRTC addresses slow intrinsic response times by imposing an extrinsic overdrive voltage for each pixel to be written, based on the prior and next pixel values and the predetermined characteristics of an LCD panel. LRTC has been implemented in LCD-based televisions by applying compensation across the entire screen, based on the assumption that the full screen is displaying motion video. LRTC is also being implemented on computer flat panel monitors, likewise applied across the entire screen, just as it is for LCD-based televisions. However, there is no requirement for LRTC to be applied to an entire screen, as no advantage is gained by applying it to static display areas. In view of the foregoing, there is a need for a system and method for selectively applying LRTC only to those areas of the screen that display video objects in motion.